1. Field of the Invention
The present invention relates to an apparatus for controlling behavior of a vehicle, more particularly, to the apparatus for controlling behavior of the vehicle during its cornering motion so as to avoid its drift-out due to its under-steering state or its spin due to its over-steering state.
2. Prior Art
An apparatus for controlling behavior of a vehicle is conventionally well known, for example, as described in the Japanese Laid-open Patent Publication No.6-183288 or No.7-223520. In the apparatus, a target yaw rate is set on the basis of a steering angle and speed of the vehicle while an actual yaw rate of the vehicle is detected using a yaw rate sensor. When deviation between the detected actual yaw rate and the target yaw rate is larger than or equal to a preset value, under-steering control for restraining an under-steering state of the vehicle or over-steering control for restraining an over-steering state of the vehicle is executed (interposed) in the vehicle controlling process.
To be concrete, the under-steering control is executed when the target yaw rate is larger than a threshold, which is such a value that a preset value is added to the actual yaw rate. On the other hand, the over-steering control is executed when the actual yaw rate is larger than a threshold, which is such a value that a preset value is subtracted from the target yaw rate.
In the conventional apparatus described above, however, there is a tendency that the under-steering control is executed excessively and frequently when the target yaw rate is larger than the threshold which is the sum of the preset value and the actual yaw rate. For example, even if the under-steering state of the vehicle falls under a so-called driven under-steering state which is caused when the is vehicle is cornering while applying the driving force of the engine to the driven wheels in accordance with the driver""s operation, it may be judged that it is running under the under-steering state resulting in the drift-out of the vehicle. In consequence, the under-steering control may be executed. In that case, the under-steering control interferes with the driven under-steering state according to the driver""s intention. In consequence, the driven under-steering state according to the driver""s intention cannot be efficiently obtained so that the driver may feel a malaise.
If the threshold for performing the under-steering control is set to a larger value, it may be prevented that the under-steering control is executed too early so that the driven under-steering state according to the driver""s intention may be obtained. In that case, however, the under-steering control may be executed too late. In consequence, it may be difficult to rapidly restrain the under-steering state resulting in the drift-out of the vehicle. So it may be unavoidable to cause the driver""s malaise due to the delay of the under-steering control.
On the other hand, when the over-steering control for restraining the over-steering state of the vehicle is executed, the following problem may occur. That is, for example, if the vehicle is one of a front wheel driving type and the engine power is lowered to cause a so-called tack-in state when the steering wheel is turned beyond a preset angle, or if there occurs a so-called counter-steering state in which the driver consciously turns back the steering wheel in the direction opposite to the vehicle-turning direction in order to restrain the over-steering state of the vehicle, it may be difficult to execute the over-steering control for restraining the tack-in state or the counter-steering state.
The present invention has been achieved in view of the above-mentioned various problems and has an object to provide a vehicle having both of higher safety and higher driving characteristics by improving the condition for executing the under-steering or over-steering control to make the control proper, thereby preventing the driver""s malaise resulting from executing the control too early or too late.
According to the first aspect of the present invention which is performed to achieve the above-mentioned object, under-steering control is executed when there has been accomplished such a condition that the steering wheel is operated in the direction to increase the steering angle and the yaw rate does not increase.
To be concrete, an apparatus for controlling behavior of a vehicle according to the first aspect of the present invention includes a controller which controls behavior of a yaw rate of the vehicle by estimating a running state of the vehicle to control a brake on the basis of estimated results. The controller executes under-steering control for restraining an under-steering state when a steering wheel is operated in a direction to increase a steering angle and the yaw rate does not increase in such a condition that the vehicle is in the under-steering state.
The condition that the steering wheel is operated in the direction to increase the steering angle and the yaw rate does not increase when the vehicle is in the under-steering state, is accomplished in the following case. That is, it is such a case that although the driver is operating the steering wheel in the direction to increase the steering angle in order to restrain the under-steering state of the vehicle, the actual yaw rate does not follow the operation, namely does not change. Therefore the apparatus may conclude that the vehicle causes a drift-out if the under-steering control is not executed. In consequence, the apparatus executes the under-steering control so that the under-steering state may be restrained.
On the other hand, under other conditions, for example such a condition that the driver is not operating the is steering wheel in the direction to increase the steering angle when the vehicle is in the under-steering state, it may be judged that the vehicle is in such driven under-steering state that the vehicle is cornering while applying the engine power to the driven wheels. In consequence, even if the vehicle is in the under-steering state, the control for restraining the state may not be executed. Therefore the under-steering control can be executed only in such a case that it is required actually and really. Thus the under-steering control may be adequately executed so that the vehicle may have both of higher safety and higher driving characteristics.
An apparatus for controlling behavior of a vehicle according to the second aspect of the present invention includes a controller which sets a target yaw rate on the basis of lateral acceleration and speed of the vehicle, and makes an actual yaw rate follow the target yaw rate. Hereupon, the controller quickens (preferentially) executing under-steering control for restraining an under-steering state of the vehicle than usual if the target yaw rate lowers by a preset value or more on an occasion that the vehicle is cornering.
That is, when the target yaw rate, which is set on the basis of the lateral acceleration and speed of the vehicle on the occasion that it is cornering, lowers by the preset value or more, it may be judged, for example, that the friction factor of the road surface rapidly changes so that the lateral acceleration decreases. In consequence, the period for executing the under-steering control is quickened. In this case also, the under-steering control may be adequately executed. In consequence, it may be prevented that the under-steering control is unnecessarily executed so that the vehicle may have both of higher safety and higher driving characteristics.
According to the third aspect of the present invention, in the apparatus for controlling the behavior of the vehicle according to the first aspect, the controller executes the under-steering control when a target yaw rate, which is set on the basis of a lateral acceleration and speed of the vehicle, lowers by a preset value or more on an occasion that the vehicle is cornering. In this case, if the steering wheel is not operated when it is judged that the friction factor of the road surface rapidly changes so that the lateral acceleration decreases, the under-steering control may be forcibly executed as same as the case of the second aspect. In consequence, the condition for executing the under-steering control may be held adequately.
An apparatus for controlling behavior of a vehicle having driven front wheels according to the fourth aspect of the present invention includes a controller which sets a target yaw rate by using at least speed of the vehicle, and makes an actual yaw rate follow the target yaw rate. Hereupon, the controller quickens executing over-steering control for restraining an over-steering state of the vehicle than usual if the vehicle is judged to be in a tack-in state.
In the apparatus having the above-mentioned construction, the period for executing the over-steering control is quickened when the vehicle of the front wheel drive type is judged to be in the tack-in state. In consequence, spin of the vehicle due to the tack-in state may be restrained at the early stage so that the condition for executing the over-steering control may be held adequately.
According to the fifth aspect of the present invention, in the apparatus for controlling the behavior of the vehicle according to the fourth aspect, the controller quickens executing the over-steering control by lowering a threshold (starting threshold) for executing the over-steering control. In this case, the over-steering control may be easily executed on the occasion of the tack-in state. Meanwhile, in the apparatus according to the sixth aspect of the present invention, the controller quickens executing the over-steering control by executing the over-steering control by force. In this case, the over-steering control may be forcibly executed on the occasion of the tack-in state. In each of the fifth and sixth aspects, the condition for executing the over-steering control on the occasion of the tack-in state may be embodied.
An apparatus for controlling behavior of a vehicle according to the seventh aspect of the present invention includes a controller which sets a target yaw rate by using at least speed of the vehicle, and makes an actual yaw rate follow the target yaw rate. Hereupon, the controller quickens executing over-steering control for restraining an over-steering state of the vehicle than usual if the vehicle is judged to be in a counter-steering state.
In the apparatus, the period for performing the over-steering control is quickened when the vehicle is judged to be in the counter-steering state. In consequence, spin of the vehicle due to the counter-steering state may be restrained at the early stage so that the condition for executing the over-steering control may be held adequately.
According to the eighth aspect of the present invention, in the apparatus for controlling the behavior of the vehicle according to the seventh aspect, the controller quickens executing the over-steering control by lowering a threshold (starting threshold) for performing the over-steering control. In this case, the over-steering control may be easily executed on the occasion of the counter-steering state. Meanwhile, in the apparatus according to the ninth aspect of the present invention, the controller quickens executing the over-steering control by executing the over-steering control by force. In this case, the over-steering control may be forcibly executed on the occasion of the counter-steering state. In each of the eighth and ninth aspects, the condition for executing the over-steering control on the occasion of the counter-steering state may be embodied.
According to the tenth aspect of the present invention, in the apparatus for controlling the behavior of the vehicle according to the seventh aspect, the controller sets the target yaw rate on the basis of lateral acceleration and speed of the vehicle, and judges the counter-steering state on the basis of a steering angle of the vehicle. In this case, the counter-steering state of the vehicle can be judged quickly and easily on the basis of the steering angle so that the period for executing the over-steering control on the occasion of the counter-steering state may be quickened.